Android system music player

Hi all:
I use the following codes to call android system music player:
Uri uri = Uri.parse(url);
Intent intent = new Intent();
intent.setDataAndType(uri, "audio/*");
intent.setAction(Intent.ACTION_VIEW);
startActivity(intent);
It can play music. But if I press back key the music stops playing.
How to call android system music player and play background?
Thank you very much!